1. Field of the Invention
The invention relates to railway maintenance equipment and, more particularly, relates to a machine capable of grinding a railway section such as a frog or other railway switch in situ. The invention additionally relates to a method of grinding a railway section using such a machine.
2. Discussion of the Related Art
Switches and other railway sections often require grinding as part of periodic maintenance or reconditioning procedures. One such railway section is a “frog.” A frog is a portion of a railway turnout or a crossing where the rails intersect to allow the wheel flanges of a rail car to cross the running rail. A typical frog includes, inter alia, a fixed or movable point forming the intersection of the converging rails, and a throat forming the juncture of the diverging rails. The typical frog is formed from a work hardening manganese casting.
The point and adjacent railway sections of a frog wear during use. Eventually, the upper horizontal surfaces and/or side flanges of the frog and the adjacent railway sections must be welded to replace the broken or worn-away frog portions. The welded portions must then be ground to return the frog surfaces to their original profile. Even before the frog wears to the point that welding is required, optimal frog maintenance requires that the horizontal and side flange surfaces be ground to remove deformed metal that could lead to more rapid frog wear or even breakage. Indeed, because frogs are typically made from a work hardening manganese steel casting, proper early maintenance could alleviate or even eliminate the need to weld the frog if the frog were initially oversized and the wheel-contacting surfaces were ground sufficiently frequently in conjunction with the work hardening process so that the frog has its ideal profile at the end of the work hardening process. The frog would thereafter wear only very gradually. Heretofore, no machine was designed to repeatedly grind frogs at this early stage of wear with high precision.
To the contrary, all previously known railway grinding machines exhibited marked drawbacks.
For instance, one common frog grinding technique requires that that the frog be removed from the railway and reconditioned in a separate maintenance facility containing welding equipment and specially designed stationary frog grinding equipment. The frog grinding equipment used by this type of facility sometimes is designed to grind both horizontal and vertical surfaces of the frog along relatively precisely defined paths, thereby obtaining a desired profile on the reconditioned frog. Machines designed to grind frogs in this manner are disclosed, e.g., in U.S. Pat. No. 3,706,856 to Keifer and U.S. Pat. No. 3,821,840 to Kershaw. These machines are effective, but require that the frog be removed from the railway for their operation. This removal requirement adds considerable expense and downtime to the frog reconditioning process. In addition, this off-site grinding technique cannot be used to effect routine maintenance on a frog that does not require complete reconditioning and also does not permit the installation or production of an initially oversized frog and the frequent grinding of that frog during the work hardening process.
Other machines are available for welding frogs in situ, i.e., without removing the frog from the associated railway section. For instance, Harsco and Plasser both have proposed large, self-propelled, track mounted machines that are used as part of a tie-gang to perform rail grinding functions in addition to other functions. A number of different grinding heads are mounted on the undercarriage of the machine and grind different surfaces of railway sections including frogs as the machine is propelled along the railway.
Sensors may be employed on the carriage to control the positioning of the various grinding heads. Machines of this type are disclosed, e.g., in U.S. Pat. Nos. 4,178,724 to Bruno and 4,908,993 to Buhler. These machines are very large and expensive to build and operate. They also lack the versatility required to precisely machine the points and other surfaces of frogs and other railway switches in situ. They are best-suited for rough grinding operations that must be followed up by hand-held grinding tools for ideal frog profiling.
Another rail grinding machine, designed specifically for frog grinding, is produced by Giesmer under the trade name MC3. The Giesmer MC3 grinder includes a workhead mounted on a carriage that rides along the track section of or in close proximity to the frog. The track sections therefore provide a reference path for carriage grinding head movement. This machine is considerably smaller, more maneuverable, and less expensive than the self-propelled machines manufactured by Harsco, Plasser, and others. However, it also has significant drawbacks and disadvantages. For instance, the rail surfaces of and immediately adjacent the frog provide a poor reference path for grinding because those surfaces deform with frog wear to the point of having pronounced low frequency undulations. Using those surfaces as a reference path during grinding produces corresponding undulations in the frog. In addition, the grinding tool of the Giesmer MC3 grinder grinds only the upper surface of the frog and adjacent rail sections using a flat stone grinder. It cannot effectively grind side surfaces of the ground railway section. It is also incapable of grinding a slope on the frog point that directs the end of the point beneath the level of the rails to assure smooth transfer of load from the frog point to the diverging rail.
Other machines designed to grind frogs and/or other railway sections in situ are disclosed in U.S. Pat. Nos. 3,377,751 to Schnyder and 6,033,166 to Hampel. These systems and other known machines share at least some of the problems with the machines discussed above, and all present other problems of their own.
The need therefore has arisen to provide a railway grinding system and/or method that can grind frogs, other switches, and possibly other sections of railways along precisely-defined grinding paths that are unaffected by the geometry of the railway section to be ground.
The need has additionally arisen to provide a railway grinding system and/or method that is sufficiently versatile to grind vertical, horizontal, and inclined surfaces of railway sections while still following a precisely defined path.
The need has a additionally arisen to provide a railway grinding system and/or method that is sufficiently versatile, precise, and unobtrusive to permit rail sections to be frequently ground in situ for the purpose of, e.g., optimizing a work hardening process.